Full duplex transmission method for high speed backplane system

ABSTRACT

A system for a backplane serializer/deserializer (SerDes) including first and second integrated circuits (IC). The first and second ICs include transmitters and receivers coupled to each other through first and second bidirectional links. A first receiver is configured to receive first data at a data rate on a first channel supported by both the first bidirectional link and the second bidirectional link. A second receiver is configured to receive second data at the data rate on a second channel supported by both the first bidirectional link and the second bidirectional link. The backplane SerDes is configured to transfer the first and second data in full duplex mode by employing two-bit pulse-amplitude modulation (PAM-4) to reduce signaling speed of the first and second bidirectional links without reducing throughput of a lane pair including the first and second channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/713,772 filed May 15, 2015 by Hiroshi Takatori, entitled“Full Duplex Transmission Method for High Speed Backplane System,” whichis a continuation of U.S. patent application Ser. No. 13/525,544 filedJun. 18, 2012 by Hiroshi Takatori, entitled “Full Duplex TransmissionMethod for High Speed Backplane System,” which claims priority to U.S.Provisional Patent Application No. 61/500,471 filed Jun. 23, 2011 byHiroshi Takatori and entitled “Full Duplex Transmission Method for HighSpeed Backplane System,” all of which are incorporated herein byreference as if reproduced in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Currently, more consumer products are intended for triple playtelecommunications, e.g., voice, video, and data communications. Toimprove such communications, high-speed networks and components arebeing developed, such as switches and routers at the Internetinfrastructure. High-speed backplane systems are one type of componentsthat serve as backbone for the network physical layer. A backplanesystem may include line cards that use serializer/deserializer (SerDes)chipsets, such as SerDes application specific integrated circuits(ASICs). A SerDes is a pair of functional blocks commonly used inhigh-speed communications to compensate for limited input/output. TheSerDes blocks convert data between serial data and parallel interfacesin both directions. The Institute of Electrical and ElectronicsEngineers (IEEE) standard 10GBASE-KR. 802.3ap defines a high-speed40-inch multi-lane backplane system at a data rate of 10 gigabits persecond (Gbps)/lane for supporting high-speed communications. Howeverdeveloping such backplane systems that have about 40 inches lane (orlink) length between line cards and reliable 10 Gbps/lane data ratesremains challenging due to stringent low noise requirements and othertechnical difficulties.

SUMMARY

In one embodiment, the disclosure includes an integrated circuit (IC)for a backplane serializer/deserializer (SerDes) system including afirst transmitter in a first IC coupled to a second transmitter and asecond receiver via a first bidirectional link, the first transmitterconfigured to send first data at a data rate to the second receiver in asecond IC via the first bidirectional link, a first receiver coupled tothe second transmitter and the second receiver via a secondbidirectional link, the first receiver configured to receive second dataat the data rate from the second transmitter in the second IC via thesecond bidirectional link, a third transmitter coupled to a fourthtransmitter and a fourth receiver via a third bidirectional link, thethird transmitter configured to send third data at the data rate to thefourth receiver in the second IC via the third bidirectional link, and athird receiver coupled to the fourth transmitter and the fourth receivervia a fourth bidirectional link, the third receiver configured toreceive fourth data at the data rate from the fourth transmitter in thesecond IC via a fourth bidirectional link. The IC is configured totransfer the first data and the second data in full duplex mode byemploying two-bit pulse-amplitude modulation (PAM-4) to reduce signalingspeed of the first bidirectional link and the second bidirectional linkwithout reducing throughput of a lane pair comprising the firstbidirectional link and the second bidirectional link. The thirdbidirectional link and the fourth bidirectional link are each configuredto transfer the third data and transfer the fourth data at the datarate.

In another embodiment, the disclosure includes a system for a backplaneserializer/deserializer (SerDes) including a first integrated circuit(IC) comprising a first transmitter and a first receiver and a second ICincluding a second transmitter coupled to the first receiver and thefirst transmitter via a first bidirectional link and a second receivercoupled to the first receiver and the first transmitter via a secondbidirectional link. The first receiver is configured to receive firstdata at a data rate on a first channel supported by both the firstbidirectional link and the second bidirectional link. The secondreceiver is configured to receive second data at the data rate on asecond channel supported by both the first bidirectional link and thesecond bidirectional link. The backplane SerDes is configured totransfer the first data and the second data in full duplex mode byemploying two-bit pulse-amplitude modulation (PAM-4) to reduce signalingspeed f the first bidirectional link and the second bidirectional linkwithout reducing throughput of a lane pair comprising the first channeland the second channel.

In another embodiment, the disclosure includes an integrated circuit(IC) for a backplane serializer/deserializer (SerDes) system including afirst transmitter in a first IC configured to send first data at a datarate to a second receiver in a second IC via a first bidirectional link,and a first receiver configured to receive second data at the data ratefrom a second transmitter in the second IC via a second bidirectionallink. The IC is configured to transfer the first data and the seconddata in full duplex mode by employing two-bit pulse-amplitude modulation(PAM-4) to reduce signaling speed of the first bidirectional link andthe second bidirectional link without reducing throughput of a lane paircomprising the first bidirectional link and the second bidirectionallink.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a schematic diagram of a typical backplane SerDes system.

FIG. 2 is a schematic diagram of an embodiment of a full duplexbackplane SerDes system.

FIG. 3 is a schematic diagram of an embodiment of a backplane fullduplex transmission method.

FIG. 4 is a schematic diagram of an embodiment of a network unit.

FIG. 5 is a schematic diagram of an embodiment of a general-purposecomputer system.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

A backplane system may comprise a group of connectors that form acomputer bus. The connectors may be connected in parallel with eachother via a plurality of pins, where each pin of each connector may becoupled to a corresponding pin in each other connector. The backplanesystem may be used as a backbone to connect multiple line cards orprinted circuit boards (PCBs) together, e.g., to establish a computer orprocessing system for network components. Other backplanes may be wirewrapped backplanes, which may be used in minicomputers and highreliability applications. A backplane system may also comprise a SerDessystem that includes transmitters and receivers, which may be coupledvia links (e.g., lanes or traces on PCBs. To meet high-speed technologyrequirements, the IEEE and optical internetworking forum (OIF) define ahigh-speed multi-lane 40-inch backplane system, as described in IEEE10GBASE-KR 802.3ap standard, which is incorporated herein by reference.The backplane system may operate at a data rate of about 10 Gbps/link ormore, which may pose challenges on the design of the backplane SerDessystem.

In other communications systems, a full duplex transmission scheme hasbeen used to increase data rates, such as in radio and telephonecommunications systems that have limited bandwidth per link. The fullduplex transmission scheme, also referred to sometimes as double duplextransmission, may double the data throughput between system componentsby enabling communications in both directions at about the same time.The data throughput between two components may be substantially doubledby doubling the number of channels per link between the two components,e.g., without increasing the bandwidth or maximum allowed data rate perlink. Specifically, each of the pair of channels on the link between thecomponents may be dedicated to transmissions in one direction. A fullduplex transmission scheme is defined in IEEE 1000BASE-T 802.3abstandard for Ethernet gigabit communications, which is incorporatedherein by reference.

Disclosed herein is a system and method for implementing the full duplextransmission for a backplane SerDes system. The system may comprise twoICs that may be coupled via one or more lanes or links, such as wires,buses, traces, or any other suitable connectors. Each link may be sharedby a transmitter and receiver pair on each end of the link. Each linkmay support a pair of bidirectional channels between a first transmitterand receiver pair on a first IC and a corresponding second transmitterand receiver pair on a second IC. The first transmitter and receiverpair, similarly the corresponding second transmitter and receiver pair,may use up to the full allowed bandwidth on the link to communicate ineach of the two directions between the two ICs.

The transmitter of the first pair on the first IC may transmit data atthe link's maximum allowed bandwidth (or data rate) to the receiver ofthe second pair on the second IC. The receiver of the first pair on thefirst IC may also receive data at the link's maximum al lowed bandwidth(or data rate) from the transmitter of the second pair on the second IC.The first and second pairs of transmitters and receivers on the two ICsmay also transmit the data simultaneously or at about the same time inopposite directions. The backplane SerDes system may be a 40-inchmulti-lane backplane system, e.g., as described in IEEE 10GBASE-KR802.3ap, and may use the full duplex transmission scheme to transmitdata, e.g., as described in IEEE 1.000BASE-T 802.3ab, at a rate of about10 Gbps/lane or more.

FIG. 1 illustrates a typical backplane SerDes system 100. The backplaneSerDes system 100 may be used as a backbone for the physical layer incurrent networks, e.g., in network nodes or servers, and may providegigabit data rates. However, the backplane SerDes system 100 may nothave sufficiently low bit error rate (BER) that meet the requirements ofa 40-inch multi-lane backplane system, e.g., as defined by IEEE10GBASE-KR 802.3ap. The backplane SerDes system may comprise a first IC110 (IC 1) that comprises a first transmitter (TX) 112 and a firstreceiver (RX) 114, a second IC 120 (IC 2) that comprises a secondtransmitter (TX) 122 and a second receiver 124 (RX), and about two pairsor links 130 (e.g., each pair of finks comprising two single lanes,wires, or traces) that couple the first IC 110 to the second IC 120.

The first IC 110 and the second IC 120 may be any circuit cards or PCBs,such as ASICs that process data. Each pair of the links 130 between thefirst IC 110 and the second IC 120 may correspond to twisted pair wiresor any other type of differential pair connectors. The two links in eachpair of links 130 may be differentially biased to transmit electricalsignals on the pair of links 130 (e.g., via a first channel in onedirection and via a second channel in an opposite direction). The firsttransmitter 112 at the first IC 110 may be coupled to the secondreceiver 124 at the second IC 120 via a first pair of links 130 (e.g.,twisted pair wires). The first receiver 114 may be coupled to the secondtransmitter 122 via a similar second pair of links 130. Each pair oflinks 130 may support about the same bandwidth and hence allow about thesame transmitted data rates between the corresponding components. Forexample, the first pair of links 130 may allow the first transmitter 112to transmit data at about 12.5 Gbps to the second receiver 124.Similarly, the second pair of links 130 may allow the first receiver 114to receive data at about 12.5 Gbps from the second transmitter 172.

Although, the backplane SerDes system 100 may be capable of providingGigabit data rates (above 10 Gbps) on each pair or links 130 betweencorresponding pairs of transmitters and receivers, this design may notmeet the BER requirements for a 40-inch multi-lane backplane system,such as defined in 10GBASE-KR 802.3ap. The BER requirements for the40-inch multi-lane backplane system that provides about 10 Gbps/lane ormore may allow a maximum margin of about 4.4 decibel (dB). The pair oflinks 130 between the ICs in the 40-inch multi-lane backplane system maybe about 40 inches long, where at such distances the crosstalk (orinterference) noise and hence the BER in the transferred signals onadjacent pairs of links 130 may become significantly high. Therelatively high noise may be associated with the relatively limitedsignal bands that may be used for transmissions. For such relativelyhigh levels of noise or errors, the data rates (e.g., 12.5 Gbps) perlink in the SerDes system 100 may not be sufficient to meet the BERrequirements for the 40-inch multi-lane backplane system. Some errorcorrections schemes have been proposed to reduce the resulting BER butmay require some level of difficulty in implementation, increase incost, and/or increase in data transfer latency. Thus, an improved designthat increases the link bandwidth may be needed.

FIG. 2 illustrates an embodiment of a full duplex backplane SerDessystem 200, which may have higher data rates per link in comparison tothe backplane SerDes system 100. The increase in data rates per link mayallow the backplane SerDes system 200 to meet the BER requirements for40-inch multi-lane backplane systems, e.g., at a maximum BER margin ofabout 4.4 dB for 10 Gbps or more data rates according to 10GBASE-KR802.3ap. The full duplex backplane SerDes system 200 may use the fullduplex transmission scheme, e.g., as described in 1000BASE-T 802.3ah, todouble the data throughput per link in comparison to the per-link datarates of the backplane SerDes system 100. The backplane SerDes system200 may comprise a first IC 210 (IC 1), a second IC 220 (IC 2), andabout four links 230 (e.g., lanes, wires, or traces) that couple thefirst IC 210 to the second IC 220, as shown in FIG. 2. The first IC 210may comprise a first transmitter 211, a first receiver 212, a secondtransmitter 213, and a second receiver 214. The second IC 220 maycomprise a third transmitter 221, a third receiver 222, a fourthtransmitter 223, and a fourth receiver 224.

The first IC 210 and the second IC 220 may be any circuit cards or PCBs,such as ASICs that process data. Each pair of links 230 between thefirst IC 210 and the second IC 220 may correspond to twisted pair wiresor any other type of differential pair connectors. The first transmitter211 and first receiver 212 at the first IC 210 may be coupled to thethird transmitter 221 and third receiver 222 at the second IC 220 via afirst pair of links 230 (e.g., twisted pair wires). The secondtransmitter 213 and second receiver 214 at the first IC 210 may becoupled to the fourth transmitter 223 and fourth receiver 224 via asimilar second pair of links 230. Each pair of links 230 may support twounidirectional channels, e.g., a first channel for transmitting signalsin the direction from the first IC 210 to the second IC 220, and asecond channel for transmitting signals in the opposite direction fromthe second IC 220 to the first IC 210. For instance, the first pair oflinks 230 (e.g., twisted pair wires) may be differentially biased at thefirst IC 210 to transmit the signals on the first channel (in a firstdirection). The same first pair of links 230 may also be electricallybiased in a differential manner at the second IC 220 to transmit thesignals on the second channel (in a second direction).

The pairs of links 230 may have about the same bandwidth and hence allowabout the same transmitted data rates between the correspondingcomponents. Based on the full duplex transmission scheme, each link 230(in a pair of links 230) may share a transmitter and receiver pair oneach link end. Each link 230 (in a pair of links 230) may enable twobidirectional channels for transferring data in the two oppositedirections between the first IC 210 and second IC 220 at about the samedata rate. To enable using the full duplex transmission scheme, each ofthe two links 230 (in the first pair of links 230) may be coupled toboth the first transmitter 211 and first receiver 212 at the first IC210 and both the third transmitter 221 and third receiver 222 at thesecond IC 220, as shown in FIG. 2. As such, the two links 230 (in thefirst pair of links 230) may allow the first transmitter 211 to transmitdata at about 12.5 Gbps (or any other gigabit rate) to the thirdreceiver 222, which may be the maximum allowed data rate per link. Thistransferred data in the direction from the first IC 210 to the second IC220 may correspond to a first channel on the first pair of links 230that uses about the maximum allowed bandwidth on the first pair of links230. The two links 230 (in the first pair of links 230) may also allowthe first receiver 212 to receive data at about 12.5 Gbps, for example,from the third transmitter 221. This transferred data in the directionfrom the second IC 220 to the first IC 210 may correspond to a secondchannel on the first pair of links 230 that may also use about themaximum allowed bandwidth on the first pair of links 230. The data maybe transferred in opposite directions on the two channels of the firstpair of links 230 at about the same time.

Similarly, each of the two links 230 (in the second pair of links 230)may be coupled to both the second transmitter 213 and second receiver214 at the first IC 210 and both the fourth transmitter 223 and fourthreceiver 224 at the second IC 220, as shown in FIG. 2. As such, the twolinks 230 (in the second pair of links 230) may allow the secondtransmitter 213 to transmit data at about 12.5 Gbps (or any othergigabit rate) to the fourth receiver 224, which may be the maximumallowed data rate per link. This transferred data in the direction fromthe first IC 210 to the second IC 220 may correspond to a first channelon the second pair of links 230 that uses about the maximum allowedbandwidth on the second pair of links 230. The two links 230 (in thesecond pair of links 230) may also allow the second receiver 214 toreceive data at about 12.5 Gbps, for example, from the fourthtransmitter 223. This transferred data in the direction from the secondIC 220 to the first IC 210 may correspond to a second channel on thesecond pair of links 230 that may also use about the maximum allowedbandwidth on the second pair of links 230. The data may be transferredin opposite directions on the two channels of the second pair of links230 at about the same time.

The full duplex backplane SerDes system may use any standard or knownfull duplex circuit for transmitting and receiving data using twochannels on the link. For instance, each pair of transmitters andreceivers in the first IC 210 and similarly the second IC 220 may beimplemented using an integrated transceiver circuit or using separatetransmitter and receiver circuits. The first IC 210 and second IC 220may be any PCBs fabricated using typical material and processes, e.g.,similar to the first IC 110 and second IC 120. In different embodiments,the first IC 210 and second IC 220 or the corresponding pairs oftransmitters and receivers that are coupled to each other via the links230 may be located on the same e cards or PCBs or on different linecards or PCBs.

As described above, using the full duplex transmission scheme may enabledoubling the data throughput per link (the overall data rate in bothdirections) without changing the signaling bandwidth (or the maximumallowed data rate) per link. The scheme may double the data throughputper link, which may be about 6 Gbps, about 10 Gbps, about 12.5 Gbps,about 20 Gbps, about 25 Gbps, or any other rate depending on the designand components used for the backplane SerDes system. Increasing the datathroughput may also increase the lifetime of the system since doing somay extend the system's usefulness over longer time in the future (wheredemand for higher speed applications is expected). Increasing thelifetime of the system is attractive in terms of reducing cost on systemupgrades. Typically, the lifetime of the system operating at about 6Gbps or about 10 Gbps is expected to be up to about three years.Doubling throughput for such data rates is expected also to double thecorresponding lifetime.

Additionally, the number of levels for line code may be increased foreach channel on the link. This may be achieved using more bits persymbol during data modulation. For instance, the full duplex backplaneSerDes system 200 may implement PAM-4 instead of one-bit pulse-amplitudemodulation (PAM-2) to signal about twice the amount of data (during thesame time window) per channel on the link. Increasing the number ofsignaled bits per symbol may further increase the data throughput perlink when combined with the full duplex transmission scheme.Alternatively, the number of bits per symbol may be increased and thetransmission data rate per channel may be decreased to maintain aboutthe same data throughput. Reducing the data rate or speed per channel orlink may reduce the amount of noise and crosstalk and hence improvesignal quality, such as for critical applications that require more dataintegrity. For example, the full duplex transmission scheme and PAM-4(instead of PAM-2) modulation may be used per link to reduce the datarate on each channel (in both directions) from about 12.5 Gbps to about6.25 Gbps without reducing the data throughput (the amount ofcommunicated data during the same time window). Reducing the data ratefrom about 12.5 Gbps to about 6.25 Gbps may substantially reduce the BERper channel.

FIG. 3 illustrates an embodiment of a backplane full duplex transmissionmethod 300, which may be used in a backplane SerDes system thatimplements the full duplex transmission scheme, such as the full duplexbackplane SerDes system 200. The method 300 may be implemented by atransmitter and receiver circuit or a transceiver circuit on an IC in abackplane SerDes system. The IC may be coupled to and configured tocommunicate with a corresponding IC on the backplane SerDes system via apair of dedicated links (e.g., lanes or traces) between the two ICs. Thelinks may have a length of about 40 inches and support Gigabit datarates, e.g., at about 10 Gbps or more, in accordance with thespecifications of 10GBASE-K.R 802.3ap.

The method 300 may begin at block 310, where one or more first symbolsmay be transmitted from a first transceiver at a first IC via a firstchannel on a pair of links at a determined data rate to a secondtransceiver at a second IC. The links may comprise a differential pairof connectors (e.g., a pair of wires) that are both shared by thetransmitting and receiving components of the transceivers on both endsof the links. The transceiver may be an integrated circuit configured totransmit and receive signals or one or more circuits that includes atransmitter and a separate receiver. For example, the first transmitter211 may transmit the data symbols via a first channel on the first pairof links 230 to the third receiver 222. The maximum allowed data ratemay be about 10 Gbps or about 12.5 Gbps. At block 320, one or moresecond symbols may be received by the first transceiver via a secondchannel on the links at about the same data rate from the secondtransceiver. For example, the first receiver 212 may receive the datasymbols via a second channel on the first pair of links 230 from thethird transmitter 221. The first symbols and the second symbols may beexchanged at blocks 310 and 320 between the first transceiver and thesecond transceiver at about the same time or at different times. Themethod 300 may then end.

FIG. 4 illustrates an embodiment of a network unit 400, which may be anydevice that transports and processes data in a network, such as aswitch, a router, or other network nodes. The network unit 400 maycomprise a backplane SerDes system as defined in 10GBASE-KR 802.3ap,such as the full duplex backplane SerDes system 200, that serves as thebackbone for physical layer communications. The network unit 400 maycomprise one or more ingress ports or units 410 coupled to a receiverRx) 412 for receiving signals and frames/data from other networkcomponents. The network unit 400 may comprise a logic unit 420 todetermine to which network components to send the packets. The logicunit 420 may be implemented using hardware, software, or both. The logicunit 420 may comprise the backplane SerDes system of the network unit400, which may implement the backplane full duplex transmission method300. The network unit 400 may also comprise one or more egress ports orunits 430 coupled to a transmitter (Tx) 432 for transmitting signals andframes/data to the other network components. The components of thenetwork unit 400 may be arranged as shown in FIG. 4.

FIG. illustrates a typical, general-purpose network component 500 thatmay correspond to or may be part of a network component, such as aserver, a switch, a router, or any other network nodes. The networkcomponent 500 includes a processor 502 (which may be referred to as acentral processor unit or CPU) that is in communication with memorydevices including secondary storage 504, read only memory (ROM) 506,random access memory (RAM) 508, input/output (I/O) devices 510, andnetwork connectivity devices 512. The general-purpose network component500 may also comprise, at the processor 502 and or any of the othercomponents of the general-purpose network component 500, a backplaneSerDes system as defined in 10GBASE-KR 802.3ap, such as the full duplexbackplane SerDes system 200.

The processor 502 may be implemented as one or more CPU chips, or may bepart of one or more ASICs. The secondary storage 504 is typicallycomprised of one or more disk drives or tape drives and is used fornon-volatile storage of data and as an over-flow data storage device ifRAM 508 is not large enough to hold all working data. Secondary storage504 may be used to store programs that are loaded into RAM 508 when suchprograms are selected for execution. The ROM 506 is used to storeinstructions and perhaps data that are read during program execution.ROM 506 is a non-volatile memory device that typically has a smallmemory capacity relative to the larger memory capacity of secondarystorage 504. The RAM 508 is used to store volatile data and perhaps tostore instructions. Access to both ROM 506 and RAM 508 is typicallyfaster than to secondary storage 504.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R₁, and an upper limit,R_(u), is disclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is a variableranging from 1 percent to 100 percent with a 1 percent increment, i.e.,k is 1 percent, 2 percent, 3 percent, 4 percent, 7 percent, . . . , 70percent, 71 percent, 72 percent, . . . , 97 percent, 96 percent, 97percent, 98 percent, 99 percent, or 100 percent. Moreover, any numericalrange defined by two R numbers as defined in the above is alsospecifically disclosed. The use of the term about means ±10% of thesubsequent number, unless otherwise stated. Use of the term “optionally”with respect to any element of a claim means that the element isrequired, or alternatively, the element is not required, bothalternatives being within the scope of the claim. Use of broader termssuch as comprises, includes, and having should be understood to providesupport for narrower terms such as consisting of, consisting essentiallyof, and comprised substantially of. Accordingly, the scope of protectionis not limited by the description set out above but is defined by theclaims that follow, that scope including all equivalents of the subjectmatter of the claims. Each and every claim is incorporated as furtherdisclosure into the specification and the claims are embodiment(s) ofthe present disclosure. The discussion of a reference in the disclosureis not an admission that it is prior art, especially any reference thathas a publication date after the priority date of this application. Thedisclosure of all patents, patent applications, and publications citedin the disclosure are hereby incorporated by reference, to the extentthat they provide exemplary, procedural, or other details supplementaryto the disclosure.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. An integrated circuit (IC) for a backplaneserializer/deserializer (SerDes) system, comprising: a first transmitterin a first IC coupled to a second transmitter and a second receiver viaa first bidirectional link, the first transmitter configured to sendfirst data at a data rate to the second receiver in a second IC via thefirst bidirectional link; a first receiver coupled to the secondtransmitter and the second receiver via a second bidirectional link, thefirst receiver configured to receive second data at the data rate fromthe second transmitter in the second IC via the second bidirectionallink; a third transmitter coupled to a fourth transmitter and a fourthreceiver via a third bidirectional link, the third transmitterconfigured to send third data at the data rate to the fourth receiver inthe second IC via the third bidirectional link; and a third receivercoupled to the fourth transmitter and the fourth receiver via a fourthbidirectional link, the third receiver configured to receive fourth dataat the data rate from the fourth transmitter in the second IC via thefourth bidirectional link, wherein the IC is configured to transfer thefirst data and the second data in full duplex mode by employing two-bitpulse-amplitude modulation (PAM-4) to reduce signaling speed of thefirst bidirectional link and the second bidirectional link withoutreducing throughput of a lane pair comprising the first bidirectionallink and the second bidirectional link, and wherein the thirdbidirectional link and the fourth bidirectional link are each configuredto transfer the third data and transfer the fourth data at the datarate.
 2. The IC of claim 1, wherein the first bidirectional link, thesecond bidirectional link, the third bidirectional link, and the fourthbidirectional link each have a length of 40 inches of printed circuitboard (PCB) trace between the first IC and the second IC.
 3. The IC ofclaim 2, wherein the third data and the fourth data are modulated byemploying PAM-4.
 4. The IC of claim 1, wherein the backplane SerDessystem is a 40-inch multi-lane backplane system defined in the Instituteof Electrical and Electronics Engineers (IEEE) 10GBASE-KR 802.3ap,standard.
 5. The IC of claim 1, wherein the data rate is equal to 6gigabit per second (Gbps), 10 Gbps, 12.5 Gbps, 20 Gbps, or 25 Gbps. 6.The IC of claim 1, wherein the first IC and the second IC are SerDesapplication specific integrated circuits (ASICs).
 7. A system for abackplane serializer/deserializer (SerDes), comprising: a firstintegrated circuit (IC) comprising a first transmitter, a firstreceiver, a third transmitter, and a third receiver; and a second ICcomprising a second transmitter coupled to the first receiver and thefirst transmitter via a first bidirectional link, a second receivercoupled to the first receiver and the first transmitter via a secondbidirectional link, a fourth transmitter coupled to the thirdtransmitter and the third receiver via a third bidirectional link, and afourth receiver coupled to the third transmitter and the third receivervia a fourth bidirectional link, wherein the first receiver isconfigured to receive first data at a data rate on a first channelsupported by both the first bidirectional link and the secondbidirectional link, the second receiver is configured to receive seconddata at the data rate on a second channel supported by both the firstbidirectional link and the second bidirectional link, the third receiveris configured to receive third data at the data rate on a third channelsupported by both the third bidirectional link and the fourthbidirectional link, and the fourth receiver is configured to receivefourth data at the data rate on a fourth channel supported by both thethird bidirectional link and the fourth bidirectional link, and whereinthe backplane SerDes is configured to transfer the first data and thesecond data in full duplex mode by employing two-bit pulse-amplitudemodulation (PAM-4) to reduce signaling speed of the first bidirectionallink and the second bidirectional link without reducing throughput of alane pair comprising the first channel and the second channel.
 8. Thesystem of claim 7, wherein the first bidirectional link and the secondbidirectional link each has a length of 40 inches of printed circuitboard (PCB) trace.
 9. The system of claim 7, wherein the first datasimultaneously traverses the first channel while the second datatraverses the second channel.
 10. The system of claim 7, wherein thefull duplex mode is a full duplex transmission scheme as defined in theInstitute of Electrical and Electronics Engineers (IEEE) 1000BASE-T802.3ab standard.
 11. The system of claim 10, wherein employing the fullduplex transmission scheme causes increased data throughput on the firstbidirectional link and the second bidirectional link without increasingbandwidth on the first bidirectional link and the second bidirectionallink.
 12. The system of claim 7, wherein employing PAM-4 increases adata throughput rate by increasing a number of signaled bits per symbolby two in comparison to employing one-bit pulse-amplitude modulation(PAM-2).
 13. An integrated circuit (IC) for a backplaneserializer/deserializer (SerDes) system, comprising: a first transmitterin a first IC configured to send first data at a data rate to a secondreceiver in a second IC via a first bidirectional link; a first receiverconfigured to receive second data at the data rate from a secondtransmitter in the second IC via a second bidirectional link; a thirdtransmitter configured to send third data at the data rate to a fourthreceiver in the second IC via a third bidirectional link; and a thirdreceiver configured to receive fourth data at the data rate from afourth transmitter in the second IC via a fourth bidirectional link,wherein the IC is configured to transfer the first data and the seconddata in full duplex mode by employing two-bit pulse-amplitude modulation(PAM-4) to reduce signaling speed of the first bidirectional link andthe second bidirectional link without reducing throughput of a lane paircomprising the first bidirectional link and the second bidirectionallink, and wherein the third bidirectional link and the fourthbidirectional link are each configured to transfer the third data andtransfer the fourth data at the data rate.
 14. The IC of claim 13,wherein the first bidirectional link, the second bidirectional link, thethird bidirectional link, and the fourth bidirectional link each have alength of 40 inches of printed circuit board (PCB) trace between the ICand the second IC.
 15. The IC of claim 14, wherein the third data andthe fourth data are modulated by employing PAM-4.
 16. The IC of claim13, wherein the backplane SerDes system is a 40-inch multi-lanebackplane system defined in the Institute of Electrical and ElectronicsEngineers (IEEE) 10GBASE-KR 802.3ap, standard.
 17. The IC of claim 13,wherein the data rate is equal to 6 gigabit per second (Gbps), 10 Gbps,12.5 Gbps, 20 Gbps, or 25 Gbps.
 18. The IC of claim 13, wherein thefirst IC and the second IC are SerDes application specific integratedcircuits (ASICs).